1. Field of the Invention
The present invention is directed to methods and devices for analyte concentration and detection using insulator-based dielectrophoresis (iDEP) and impedance-based particle detection (IM).
2. Description of the Related Art
Bioterrorism demands rapid and accurate monitoring of water and the environment for safety and quality. To detect bioagents at low concentrations in samples, techniques that selectively, accurately and rapidly collect, concentrate and detect the bioagents are necessary. Unfortunately, prior art methods take fifteen to twenty minutes before detection. See Stachowiak et al (2005) ASME Internat'l Mech. Engineer. Congress Exp., Orlando, Fla.
Dielectrophoresis (DEP) allows the rapid collection of analytes from large volume samples as compared with conventional mechanical filtering approaches. DEP is the motion of particles driven by conduction effects in a nonuniform electric field which can be used to transport suspended particles with either oscillating (AC), steady (DC), or mixed AC/DC electric fields. DEP may be used to collect specific types of particles rapidly and reversibly based on their size, shape, conductivity and polarizability.
Many device architectures and configurations have been developed to sort a wide range of biological particles by DEP. Typical dielectrophoretic devices employ an array of thin-film interdigitated electrodes placed within a flow channel to generate a nonuniform electric field that interacts with particles near the surface of the electrode array. See Yang et al. (1999) Anal. Chem. 71(5):911-918. These electrode-based DEP devices have been shown to be effective for separating and concentrating cells, proteins, DNA, and viruses. See Markx et al. (1994) J. Biotech. 32(1):29-37; Zheng et al. (2004) Biosens. Bioelect. 20:606; Washizu et al. (1990) IEEE Trans. Indust. Appl. 26:1165-1171; and Akin et al. (2004) Nano Lett. 4(2):257-259.
The concept of DEP coupled with impedance measurements (DEPIM) was first introduced by Suehiro et al. See Suehiro et al. (2003) J. Electrostatics 57(2):157-168; Suehiro et al. (2001) IEEE 36th Annual Meeting of the Industry-Application-Society (IAS), Chicago, Ill.; Suehiro et al. (2003) J. Electrostatics 58(3-4):229-246; and Suehiro et al. (2003) Sensors and Actuators B: Chemical 96(1-2):144-151. Suehiro et al. showed that impedance measurements can be effective to detect electroporation of cells and to specifically detect bacteria with a combined antibody-antigen reaction.
Unfortunately, DEPIM is problematic for various reasons including those associated with conventional DEP. The problems encountered are associated with microfabricated electrodes that are used to separate and concentrate submicron particles as the electrodes generate large electric fields in their proximity. The large electric fields and electrochemical effects may cause fouling, e.g. clumping of particles and affixation to channel walls and electrode surfaces, which detrimentally affect performance. Further, channel heights of prior art DEP devices are limited as they are dependent on the rapid dissipation of electric fields above electrode surfaces. Thus, high-throughput of particles using conventional DEP methods is limited.
Suehiro (2003) describes DEP trapping using interdigitated electrodes. Particles are detected by measuring impedance changes that determine the presence of “pearl chains,” linear clusters of particles formed by dipolar alignment. These clusters of particles are formed at the site of trapping. The impedance changes occur as a result of these pearl chains forming an electrical connection between electrodes. The conductive properties of the particles relative to those of the suspending medium determine the observed changes in impedance. The electrodes are metal (chrome) and are not passivated. Suehiro discusses coating with antibodies to promote adhesion to the electrode surface.
The challenge with using traditional DEP and impedance measurement by employing collocated electrodes is that the system cannot have very high volumetric throughput coupled with a likelihood of chip fouling. These limitations arise because the power needed to drive DEP with high throughput would induce delamination of the electrodes due to thermal expansion from joule heating. Additionally, the drive frequency for the DEP device may be fundamentally different than what is used for the IM in terms of both amplitude and frequency.
Thus, a need still exists for methods and devices suitable for the rapid and continuous concentration, delivery, and detection of low concentration analytes.